One of the problems faced by the perfumery industry lies in the relatively rapid loss of the olfactive benefit provided by odoriferous compounds due to their volatility, particularly that of “top-notes”. This problem is generally tackled using a delivery system, e.g. capsules containing a perfume, to release the fragrance in a controlled manner.
Polyurea capsules, formed by polymerisation between a polyisocanate and a polyamine, are well known in the art. However, such delivery systems may suffer from stability problems, in particular when incorporated into surfactant based products such as detergents, which are strongly aggressive towards said delivery systems.
It is especially difficult to have a good stability and a good dispersion of the capsules altogether. The efficiency of the capsules, as well as their perfume retention ability, are in particular dependent on the stability of the capsules in the product base. On the other hand, their dispersion is very important because the aggregation of capsules increases the tendency of the capsule-containing product to phase separate, which is an important disadvantage.
Another important problem faced by the perfumery industry is to provide delivery systems that are well deposited on the substrate for the treatment of which they are intended to be used, such as textile, skin, hair or other surfaces. To address this problem, the use of cationic capsules has been proposed in the prior art. Cationic capsules are also known to be better dispersed in several applications.
For example, WO 01/41915 discloses a process for the preparation of capsules carrying cationic charges. Such a process is allegedly applicable to a large variety of microcapsules, in particular polyurethane-polyurea microcapsules are mentioned. After their formation, the capsules are placed in a medium which is favourable for the treatment with cationic polymers. The treatment with cationic polymers is carried out after purification of the basic capsule slurry, in order to eliminate anionic or neutral polymers which were not incorporated in the capsule wall during formation thereof, and other free electrically charged compounds involved in the encapsulation process. In particular, the capsules are diluted, isolated and then resuspended in water, or even washed to further eliminate anionic compounds. After the purification step, the capsules are agitated vigorously and the cationic polymers are added. Partially quaternized copolymers of polyvinylpyrrolidones are cited to this purpose, among many other suitable polymers. The described process comprises several steps following the capsule formation, said process being therefore time consuming and not economically profitable.
US 2006/0216509 also discloses a process for the cationization of polyurea capsules. This process involves the addition, during the wall formation, of polyamines, the capsules thus bearing latent charges, depending on the pH of the medium. Once formed, the capsules are subsequently cationized by acid action or alkylation to bear permanent positive charges. The cationic compounds therefore react with the capsule wall, chemically changing the latter.
Several other prior art documents disclose polyurea microcapsules, but these are not cationic. For example, U.S. Pat. No. 5,225,118 discloses polyurea microcapsules comprising a colloidal stabilizer in the form of an aqueous solution of polyvinyl alcohol and polyvinyl pyrrolidone but this stabilizer is not cationic and thus the microcapsules do not bear any positive charge. The microcapsules of the invention show a better deposition on the surface on which they are applied and further show a better dispersion in product bases.
Another example is WO 2007/004166 which describes polyurea microcapsules comprising polyvinyl alcohol and an anionic surfactant. Again, these microcapsules are not cationic. To the contrary, they are anionic and therefore have different properties when compared to the microcapsules of the invention. In particular, the microcapsules of the invention have the surprising and advantageous effect of being better dispersed in product bases, especially in unstructured liquid detergents.
The present invention provides a new simplified process for the preparation of polyurea microcapsules. It advantageously solves the problem of providing a single-step process for preparing polyurea microcapsules bearing permanent positive charges, the capsules being stable, well dispersed in product bases and well deposited on the substrate on which the perfumed product is applied. As a single-step process, we mean a process that does not involve any further step, after the capsule formation, unlike what is the case in the prior art.
None of the above-cited prior art documents teaches the use of a specific stabilizer in the process of the present invention, as described below, and in particular not the specific proportions of the polymers forming said stabilizer.